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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [MCA][ARM] Assertion failed regarding CarryOver value in the DispatchStage"
href="https://bugs.llvm.org/show_bug.cgi?id=50174">50174</a>
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<th>Summary</th>
<td>[MCA][ARM] Assertion failed regarding CarryOver value in the DispatchStage
</td>
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<th>Product</th>
<td>tools
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>llvm-mca
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>minyihh@uci.edu
</td>
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<th>CC</th>
<td>andrea.dibiagio@gmail.com, llvm-bugs@lists.llvm.org, matthew.davis@sony.com
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<p>
<div>
<pre>Hi,
When I use the following two instructions as the input:
```
pop {r3, r4, r5, r6, r7, pc}
nop
```
With the following command:
```
$ llvm-mca -mtriple="thumbv7-gnueabihf-linux" -mcpu="cortex-a57" input.s
```
MCA crashes with the following message:
```
llvm-mca: /path/to/llvm-project/llvm/lib/MCA/Stages/DispatchStage.cpp:79:
llvm::Error llvm::mca::DispatchStage::dispatch(llvm::mca::InstRef): Assertion
`!CarryOver && "Cannot dispatch another instruction!"' failed.
```
After digging into it a little bit, I think the problem is that EntryStage
should wait until DispatchStage finish all its carried-over micro-ops (i.e.
until CarryOver == 0) before pumping in another instruction. Originally the
pipeline uses `isAvailable` method in each stage to implement this flow control
/ guard. But `DispatchStage::isAvailable` seems to fail in this case.</pre>
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